1. Field of the Invention
The present invention relates to an apparatus and method for effecting an operation on at least one continuously moving web or piece attached to a continuously moving web using a rotating function roll. The invention more particularly concerns an apparatus and method for ultrasonically bonding at least one continuously moving web using a rotary ultrasonic horn.
2. Description of the Related Art
Several different conventional methods have existed for effecting an operation on at least one continuously moving web using a rotating function roll. Such operations have included bonding, cutting, perforating, splicing, compacting and the like which may or may not be intermittent.
For example, it has been well known to those skilled in the art to bond at least one continuously moving substrate web by constrictively passing it between a rotating bonding roll and a rotating anvil roll. Typically, the anvil roll has included a plurality of raised projections that have been configured to bond the web in a predetermined bond pattern. The substrate web has been bonded by any means known to those skilled in the art such as thermal, ultrasonic or adhesive bonding. For example, the bonding roll has been heated to thermally bond the web as the web constrictively traveled between the bonding roll and the anvil roll. Alternatively, the bonding roll has included a rotary ultrasonic horn that has been capable of transmitting ultrasonic energy to ultrasonically bond the web as it constrictively traveled between the rotary ultrasonic horn and the anvil roll. Representative examples of rotary ultrasonic horns that have been used to bond at least one web are described in commonly assigned U.S. Pat. No. 5,096,532 to Neuwirth et al. issued Mar. 17, 1992; and U.S. Pat. No. 5,110,403 to Ehlert issued May 5, 1992.
The consistency and quality of the bond when using such rotary bonding techniques is dependent upon the force exerted on the web by the anvil roll and bonding roll; the time that the web is being pressed which is dependent upon the operating speed; and the types of materials being bonded. In thermal bonding methods, the consistency and quality of the bonds has also been dependent on the temperature of the bonding roll. In ultrasonic bonding methods, the consistency and quality of the bonds has also been dependent on the frequency and amplitude of the vibrations of the ultrasonic horn.
Many of the conventional methods for rotary bonding have included a rotating bonding roll that is mounted in a cantilevered configuration such that the bonding roll is not supported about its surface. However, such conventional methods have not always been sufficiently satisfactory. The use of a cantilevered bonding roll has some inherent limitations that adversely affect the bond quality that, in turn, limits the operating speeds. When the bonding roll is mounted in a cantilevered configuration, the consistency and quality of the bond is dependent upon the runout in both the bonding roll and the anvil roll and the amount that both rolls flex when under a variable load due to the types of materials being bonded and the variable operating speeds. In such a configuration, it has been virtually impossible to maintain a proper interference between the bonding roll and the anvil roll to achieve the desired constant force between the rolls in the bond region especially as the process variables change. Thus, in many of the conventional methods for rotary bonding, the bond quality has been undesirably variable both along the length and across the width of the bond region and the process has not been as robust as desired in a manufacturing environment.
The consistency and quality of the bonds when rotary bonding using conventional methods has been particularly variable if the desired bond pattern is intermittent because it becomes increasingly difficult to maintain the constant force and contact between the bonding and anvil rolls along the entire length of the bond pattern. When using many of the conventional methods for rotary bonding in such a configuration, the bond quality has typically been less than satisfactory along the length of the bond pattern. This inconsistency has been due, at least in part, to excessive interference at the leading edge of the intermittent pattern and insufficient interference at the trailing edge of the intermittent pattern as the bonding roll flexes and deflects or bounces. Both the excessive interference and the insufficient interference have resulted in poor bond quality and consistency.
Many of the conventional methods for rotary bonding have used different approaches to diminish the extent of these limitations. For example, the bonding roll, anvil roll and support frames have been precisely machined to minimize the runout in the bonding system. In addition, the strength of the bonding and anvil rolls and their support frames has been increased to minimize the flexing under the variable load conditions. However, these approaches have been expensive and inefficient and have required extensive setup modifications as the process variables, such as operating speed, are changed.
The above-mentioned difficulties of maintaining the desired bond quality and consistency have been even more acute when ultrasonically bonding at least one continuously moving web using a rotary ultrasonic horn. The rotary ultrasonic horn has inherent movement which may adversely affect bond consistency and quality because it continuously vibrates at a given frequency and amplitude to efficiently bond the web. Because the ultrasonic horn has to vibrate at its resonant frequency like a bell it cannot be rigidly mounted. The need to provide non-rigid mounts produces deflections under load. Moreover, the rotary ultrasonic horn has usually been mounted in a cantilevered configuration that enhances the amount of flex under load.
These difficulties are even further exasperated when the rotary ultrasonic bonding includes an intermittent bond pattern as discussed above.